The use of lasers has become increasingly widespread. Lasers can be used for manufacture of products, material analysis, etc. Chemical imaging is one form of material analysis. Chemical imaging using mass spectrometry has attracted increasing interest because of numerous applications for characterizing materials science samples, biological tissues, individual aerosol particles, minerals, forensic evidence, etc. Chemical imaging is often based on secondary ion mass spectrometry (SIMS) by bombarding a surface with atomic primary beams to yield elemental secondary ions from a surface being analyzed. One disadvantage of such techniques includes surface charging that can lead to redeposition of material. Further, for SIMS, chemical imaging usually uses atomic ion primary beams that provide primarily elemental and not molecular chemical information.
Recently, laser desorption (LD) techniques for mass spectrometry have attracted attention because they produce intact molecular ions, avoid surface charging issues, and allow tuning of laser irradiation (wavelength and fluence) to accommodate various sample types. Careful control of laser fluence prevents excessive sputtering that can contaminate adjacent locations of a sample also intended for analysis.
Traditionally, LD microprobe mass spectrometers use scanning techniques that rely on manipulation of a sample target. Alternative LD techniques may accomplish manipulation by moving optical components. In such cases, spatial resolution (minimum controlled displacement of laser energy on the sample target) has been limited to mechanical resolution (minimum controlled displacement per step) of stepper or servo motors used to move the sample target or optical components. Such techniques often encounter problems with reproducible alignment of laser scans with sample targets. Often, such techniques are not easily amenable to analysis under extreme conditions including confined space, high magnetic fields, operation under vacuum, operation under high pressure, operation under hazardous conditions, etc.